1. Field of the Invention
The present invention relates to an ink suitable for use in recording by an ink-jet system or with a writing utensil, and a recording method, instruments and recording apparatus using such an ink.
2. Related Background Art
Inks with any of various dyes or pigments dissolved or dispersed in water or a liquid medium composed of water and an organic solvent have heretofore been used as inks for ink-jet recording or writing utensils.
Inks to be used in ink-jet recording systems are required to have the following performance characteristics:
(1) providing images sufficient in optical density; PA1 (2) being able to quickly fix on a recording medium and causing no feathering; PA1 (3) causing no clogging at an orifice; PA1 (4) being able to stably conduct recording even upon continuous recording or resumption of recording after left to stand for a long period of time; PA1 (5) undergoing no changes of physical properties even after stored for a long period of time; PA1 (6) causing no problem about the safety of users; and PA1 (7) exerting no adverse influence on means for generating thermal energy in an ink-jet system making good use of thermal energy. PA1 (8) providing an even color solid print causing no color irregularity; and PA1 (9) even when stopping ejection of an ink of a specific color from a specific nozzle for a predetermined period of time to use it in a part of a print to be produced, causing no ejection failure upon resumption of the ejection.
Besides the requirements (1) to (7), they are also required to have the following properties for the purpose of conducting color recording:
In order to satisfy the above-described requirements, it has been already reported in Japanese Patent Application Laid-Open Nos. 49-27732, 57-94066 and 58-2365 to add urea or any of various urea derivatives to an ink.
In order to prevent drying at a pen point, it has also been disclosed in Japanese Patent Application Laid-Open No. 4-331272 to use chitosan or N-carboxymethylchitosan.
However, the above prior art involves the following problems.
First, when urea is used, urea itself has low thermal stability though it has sufficient moisture retention, so that it is decomposed to generate carbon dioxide and ammonia. Accordingly, an ink to which urea is added is excellent in resistance to clogging and ejection stability as initial performance, but cannot last the initial performance when stored over a long period of time.
Second, it has been proposed to use urea derivatives, in which the hydrogen atoms of urea have been substituted by various substituents for the purpose of improving the thermal stability of urea. However, the use of such urea derivatives cannot bring about the same effects as urea has. More specifically, the moisture retention of urea is derived directly from the hydrophilicity of the amino groups in urea. Therefore, the substitution of a part of the hydrogen atoms of the amino groups by a alkyl group or the like reduces the effects characteristic of urea. In addition, urea and the urea derivatives have poor affinity for fibers, so that they do not contribute to improvement of the evenness of solid areas in images formed by ink-jet recording on various kinds of non-coated paper such as commercially-available paper for copying and bond paper, i.e., so-called plain paper.
Finally, the mere inclusion of conventionally-known chitosan or N-carboxymethylchitosan into an ink cannot improve the water fastness of the resulting recorded images.